Ethylene copolymers and process for production

ABSTRACT

A new ethylene copolymer comprising: a repeating unit (A) represented by the formula: -CH2-CH2-; a repeating unit (B) represented by the formula:  &lt;IMAGE&gt;  (wherein R1 is defined as hereinbefore), and a repeating unit (C) represented by the formula:  &lt;IMAGE&gt;  (wherein R2 and R3 are defined as hereinbefore), said repeating units (A), (B) and (C) being orientated in a random and straight chain arrangement, said repeating unit (B) content being 0 to 45 mol %, said repeating unit (C) content being 0.001 to 45 mol %, and said copolymer having a weight average molecular weight of at least 5,000. A process for producing said ethylene copolymer by using a catalyst containing a specific chromium compound.

BACKGROUND OF THE INVENTION

The present invention relates to ethylene copolymers having a novelstructure and a process for the production thereof. More particularly,it is concerned with ethylene copolymers which comprises a straightchain base polymer of an ethylene unit with an unsaturated carboxylicacid or its ester unit orientated in a random arrangement in theethylene base polymer and, if desired, further with a small amount ofalkyl side chains bonded to the ethylene base polymer, and to a processfor efficiently producing the above ethylene copolymers.

As copolymers of ethylene and unsaturated carboxylic acid or its esters(e.g., acrylic acid esters), copolymers produced by the high pressureradical polymerization method or the low pressure Ziegler method havebeen known. Copolymers produced by the high pressure radicalpolymerization method have such a structure that the unsaturatedcarboxylic acid or its ester radical is orientated in the ethylene chainin a random arrangement. It is known, however, that in accordance withthe high pressure radical polymerization method, monomers are notcopolymerized in a straight chain arrangment; there are obtained onlybranched copolymers. On the other hand, in copolymers produced by thelow pressure Ziegler method using titanium, zirconium and a vanadiumcompound as catalyst components, the unsaturated carboxylic acid or itsester is bonded to the ethylene polymer chain in a block copolymerarrangement. That is, by any of the conventional polymerization methodincluding the high pressure radical polymerization method and the lowpressure Ziegler method, copolymers in which the ethylene unit and theunsaturated carboxylic acid or its ester unit are arranged in a randomconfiguration have not be obtained.

SUMMARY OF THE INVENTION

An object of the present invention is to provide ethylene copolymershaving a novel structure that an unsaturated carboxylic acid or itsester unit is copolymerized in a random arrangement, an ethylene polymerchain is in a straight chain arrangement, and further a small amount ofalkyl side chains are bonded to the ethylene base polymer chain.

Another object of the present invention is to provide a process forefficiently producing the above copolymers.

That is, the present invention relates to an ethylene copolymercomprising:

a repeating unit (A) represented by the formula (I):

    --CH.sub.2 --CH.sub.2 --                                   (I)

a repeating unit (B) represented by the formula (II):

    --CH.sub.2 --CH--                                          (II)

(wherein R¹ represents an alkyl group having 1 to 20 carbon atoms); and

a repeating unit (C) represented by the formula (III): ##STR3## (whereinR² represents a hydrogen atom, a halogen atom, an alkyl group having 1to 20 carbon atoms, an alkenyl group having 3 to 20 carbon atoms, acycloalkyl group having 3 to 20 carbon atoms, an aryl group having 6 to20 carbon atoms or an aralkyl group having 7 to 20 carbon atoms, and R³represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms,an alkenyl group having 3 to 20 carbon atoms, a cycloalkyl group having3 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms or anaralkyl group having 7 to 20 carbon atoms), said repeating units (A),(B) and (C) being orientated in a random and straight chain arrangement,said repeating unit (B) content being 0 to 45 mol%, said repeating unit(C) content being 0.001 to 45 mol%, and said copolymer having a weightaverage molecular weight of at least 5,000.

Furthermore, the present invention relates to a process for producingthe above ethylene copolymer which comprises copolymerizing ethylene andunsaturated carboxylic acid or its ester represented by the formula(IV): ##STR4## (wherein R² and R³ are the same as defined above) by theuse of a catalyst containing (a) a transition metal compound and (b) anorganometallic compound as main components and further in the presenceof a Lewis acid, wherein the transition metal compound (a) is at leastone chromium compound selected from chromium carboxylic acid salts,chromium alkoxy compounds, chromium chelate compounds, chromiumπ-complexes, chromium aryl compounds and chromium halide, and theorganometallic compound (b) is at least one compound selected from theorganic compounds of Groups I to V metals of the Periodic Table.

DETAILED DESCRIPTION OF THE INVENTION

The ethylene copolymer of the present invention comprises the repeatingunit (A) represented by the formula (I) (ethylene unit), the repeatingunit (B) represented by the formula (II) (α-olefin unit) and therepeating unit (C) represented by the formula (III) (unsaturatedcarboxylic acid or its ester unit), or the repeating unit (A) and therepeating unit (C) only, which are arranged in a straight chain form.

The ethylene copolymer of the present invention will hereinafter beexplained in detail.

The ethylene copolymer of the present invention basically comprises therepeating unit (A), ethylene unit, polymerized in a straight chainarrangement, and the repeating units (B) and (C) are bonded orcopolymerized to the ethylene unit in a straight chain arrangementwithout formation of a side chain or branch, thereby forming as a wholea straight chain copolymer as the principle chain in which a side chainresulting from an alkyl group represented by R¹ of the repeating unit(B) is linked to the principle chain. Furthermore, in the ethylenecopolymer of the present invention, almost no side chain other than thatresulting from R¹ exists and the side chain is directly bonded to theprinciple chain; that is, the ethylene copolymer of the presentinvention does not have a complicated structure containing double ortriple branches other than the side chain resulting from R¹.

The ethylene copolymer of the present invention includes copolymers nothaving the repeating unit (B), i.e., copolymers not having an alkyl sidechain resulting from R¹.

Furthermore, in the principle chain of the ethylene copolymer of thepresent invention, there is almost no region where the repeating unit(B) or (C) is copolymerized in a block arrangement.

In the ethylene copolymer of the present invention, the repeating unit(B) content is 0 to 45 mol%, preferably 0 to 30 mol% and more preferably0 to 15 mol%, the repeating unit (C) content is 0.001 to 45 mol%,preferably 0.1 to 30 mol% and more preferably 1 to 15 mol%, and theweight average molecular weight is at least 5,000 and preferably 10,000to 3,000,000.

The repeating unit (B) represented by the general formula (II) variesdepending on the type of R¹.R¹ is an alkyl group having 1 to 20 carbonatoms, specifically a methyl group, an ethyl group, a n-propyl group, aniso-propyl group, a n-butyl group, an iso-butyl group, a tert-butylgroup, a n-pentyl group, a n-hexyl group, a n-octyl group and the like.

The repeating unit (C) represented by the general formula (III) variesdepending on the types of R² and R³. More specifically, it includes anacrylic acid unit, a methyl acrylate unit, an ethyl acrylate unit, an-propyl acrylate unit, an iso-propyl acrylate unit, a n-butyl acrylateunit, an iso-butyl acrylate unit, a tert-butyl acrylate unit, a n-hexylacrylate unit, a n-octyl acrylate unit, a 2-ethylhexyl acrylate unit, abenzyl acrylate unit, a methacrylic acid unit, a methyl methacrylateunit, an ethyl methacrylate unit, a n-propyl methacrylate unit, aniso-propyl methacrylate unit, a n-butyl methacrylate unit, an iso-butylmethacrylate unit, a tert-butyl methacrylate unit, a 2-ethylhexylmethacrylate unit, a phenyl methacrylate unit, a methyl α-chloroacrylateunit, an ethyl α-chloroacrylate unit, and a methyl α-phenylacrylateunit.

The ethylene copolymer of the present invention can be produced byvarious methods. Usually the ethylene copolymer of the present inventionis produced by copolymerizing ethylene and unsaturated carboxylic acidor its ester represented by the general formula (IV) described above. Inthis reaction, ethylene as one of the starting materials constitutes therepeating unit (A) represented by the formula (I). Depending on reactionconditions, ethylene is partially polymerized in a branched arrangement,thereby forming the repeating unit (B) represented by the formula (II).In this case, R¹ of the formula (II) becomes an alkyl group having 1 or2 carbon atoms, i.e., a methyl group or an ethyl group and does notalmost form a long chain alkyl group having 3 or more carbon atoms.Furthermore, the proportion of the repeating unit (B) represented by theformula (II) is relatively small and in some cases, the repeating unit(B) does not exist at all.

In a case where the repeating unit (B) content of the ethylene copolymeris intended to increase, and/or in a case where R¹ of the formula (II)is not limited to a methyl group and an ethyl group and is intended tomake a long chain alkyl group, it sufficies that as starting materials,along with ethylene and the unsaturated carboxylic acid or its ester ofthe general formula (IV), α-olefins having 3 or more carbon atoms,particularly α-olefins having 3 to 22 carbon atoms are used depending onthe type of the desired ethylene copolymer. α-Olefins which can be usedinclude propylene, 1-butene, 1-pentene, 1-hexene, 1-octene,3-methylbutene-1, 4-methylpentene-1 and 1-decene. The type of theα-olefin is determined appropriately depending on the number of carbonatoms contained in R¹ of the formula (II).

In accordance with the process of the present invention, the aboveethylene copolymer is produced by copolymerizing the above startingmaterials by the use of a catalyst containing the transition metalcompound (a) and the organometallic compound (b) as main components. Asthe transition metal compound (a), one or more chromium compoundsselected from chromium carboxylic acid salts, chromium alkoxy compounds,chromium chelate compounds, chromium π-complexes, chromium arylcompounds and chromium halide are used. As the organo-metallic compound(b), at least one compound selected from the organic compounds of GroupsI to V metals is used.

The catalyst which is used in the present invention, comprising thetransition metal compound (a) and the organo-metallic compound (b) isdescribed below in detail.

Chromium carboxylic acid salts include, as well as the carboxylic acidsalts of chromium, their carboxylic anhyride adducts, ester adducts,ether adducts and ketone adducts. As the chromium carboxylic acid salts,compounds represented by the general formulae: Cr(OCOR⁴)₃,Cr(OCOR⁴)₃.(R⁵ OR₆)_(n), Cr(OCOR⁴)₃, Cr(OCOR⁴).R⁹ (COOR¹⁰)₂,Cr(OCOR⁴)₃.(R¹¹ ₂ CO)_(n) and Cr(OCOR⁴)₃.[R¹² CO)₂ O]_(n) (wherein R⁴ toR¹² each represent an alkyl group having 1 to 20 carbon atoms, analkenyl group, a vinyl group, a cycloalkyl group, an aryl group, ahaloalkyl group, an aralkyl group or a hydrogen atom, and n represents asolid number of 1 or more. More specifically, aliphatic carboxylic acidsalts such as Cr(CH₃ COO)₃, Cr(C₁₇ H₃₅ COO)₃, aromatic carboxylic acidsalts such as Cr(C₆ H₅ COO)₃ and Cr(CH₃ C₆ H₆ COO)₃, and the carboxylicanhydride adducts, ester adducts, ether adducts, ketone adducts and thelike of the above carboxylic acid salts can be used. These adductsinclude fatty acid anhydrides such as acetic anhydride, propionicanhyride, butyric anhydride, iso-butyric anhyride, valeric anhyride andiso-valeric anhyride, aromatic acid anhydrides such as benzoic anhyride,toluic anhyride, cinnamic anhydride, phthalic anhyride and maleicanhyride, aliphatic esters such as methyl formate, ethyl formate, propylformate, butyl formate, methyl acetate, ethyl acetate, propyl acetate,butyl acetate, hexyl acetate, octyl acetate, benxyl acetate, vinylacetate, phenyl acetate, benzyl acetate, cyclohexyl acetate, methylpropionate, ethyl propionate, propyl propionate, butyl propionate, octylpropionate, phenyl propionate, benzyl propionate, methyl butyrate, ethylbutyrate, propyl butyrate, amyl butyrate, octyl butyrate, methylvalerate, ethyl valerate, propyl valerate, butyl valerate, methylacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methylmethacrylate, ethyl methacrylate, butyl methacrylate, methylchloroacetate, ethyl dichloroacetate, ethyl crotonate, ethyl pivalate,dimethyl maleate and ethyl cyclohexanecarboxylate, aromatic esters suchas methyl benzoate, ethyl benzoate, propyl benzoate, butyl benzoate,octyl benzoate, cyclohexyl benzoate, benzyl benzoate, methyl toluate,ethyl toluate, ethyl ethylbenzoate and ethyl anisate, ethers such asmethyl ether, ethyl ether, isopropyl ether, n-butyl ether, amyl ether,tetrahydrofuran, anisole and diphenyl ether, and ketones such asacetone, methyl ethyl ketone, methyl isobutyl ketone, acetophenone,benzophenone and benzoquinone.

As chromium alkoxy compounds, compounds represented by the generalformula (V):

    Cr(OR.sup.13).sub.4-m.sup.X' m                             (V)

are usually used. In the general formula (V), R¹³ represents an alkylgroup having 1 to 20 carb on atoms, an alkenyl group, a cycloalkylgroup, an aryl group or an aralkyl group. Representative examples of thegroups represented by R¹³ are a methyl group, an ethyl group, a n-propylgroup, an iso-propyl group, a n-butyl group, an iso-butyl group, a hexylgroup, a 2-ethylhexyl group and a phenyl group. X¹ represents a halogenatom (e.g., a chlorine atom, a bromine atom and an iodine atom). mrepresents a real number satisfying the relation of 0 ≦m<4.

Representative examples of the compounds represented by the generalformula (V) are tetramethoxychromium, tetraethoxychromium,tetra-n-butoxychromium, tetra-iso-butoxychromium,tetra-tert-butoxychromium, tetrahexyloxychromium,tetrastearyloxychromium, tetraphenoxychromium, triethoxychromiummonochloride, diethoxychromium dichloride, tri-n-butoxychromiummonochloride, and tri-n-butoxychromium monochloride.

The above chromium chelate compounds include chromiumtrisacetylacetonate represented by the formula: Cr(acac)₃, chromiumtris(2-methyl-1,3-butanediol) represented by the formula: Cr(mbd)₃, andchromium tris(1,3-butanedionate) represented by the formula: Cr(bd)₃.The symbol "acac" indicates an acetylacetonate group, and chromiumtrisacetylacetonate has the following structural formula: ##STR5## Thesymbol "mbd" indicates a 2-methyl-1,3-butanedionate group, and chromiumtris(2-methyl-1,3-butanedionate) has the following structural formula:##STR6## The symbol "bd" indicates a 1,3-butanedionate group, andchromium tris(1,3-butanedionate) has the following structural formula:##STR7## The above chromium π-complex compounds include aromatic ringπ-complex compounds such as biscyclopentadienylchromium represented bythe formula: (cp)₂ Cr (wherein the symbol "cp" indicates acyclopentadienyl group), bisbenzenechromium represented by the formula:(C₆ H₆)₂ Cr, diphenylbenzenechromium represented by the formula: (2C₆H₅) (C₆ ^(H) ₆)Cr, dihexamethylbenzenechromium represented by theformula: ##STR8## π-cyclopentadienylbromochromium acetylacetonaterepresented by the formula: ##STR9## π-cyclopentadienyl(benzene)chromiumrepresented by the formula: ##STR10## andπ-cyclopentadienyl-π-cycloheptadienylchromium represented by theformula: ##STR11## and π-allyl complex compounds such astris(η-allyl)chromium and tetrakis(η-allyl)chromium.

The above chromium aryl compounds include diphenylchromium andtetraphenyltristetrahydrofuran chromium.

Preferred examples of the above chromium halide are compoundsrepresented by the general formula: CrX² _(n) (wherein X² indicates ahalogen atom, and n indicates 2 or 3). Examples of these compounds arechromium trichloride, chromium tribromide, chromium triiodide, chromiumdichloride, chromium dibromide and chromium diiodide.

In the present invention, as the transition metal compound (a), at leastone compound selected from the specified chromium compounds as describedabove is used.

As the organometallic compound (b), at least one compound selected fromGroups I to V metal-containing organic compounds is used. These Groups Ito V metal-containing organic compounds include compounds represented bythe general formula (VI):

    R.sub.k MX.sup.3.sub.i-k                                   (VI)

In the general formula (VI), R represents an alkyl group having 1 to 20carbon atoms, an alkenyl group, a cycloalkyl group, an aryl group or anaralkyl group. Representative examples of the groups represented by Rare a methyl group, an ethyl group, a n-propyl group, an iso-propylgroup, a n-butyl group, an iso-butyl group, a hexyl group, a2-ethylhexyl group and a phenyl group. M represents lithium, sodium,potassium, magnesium, zinc, cadmium, aluminum, boron, gallium, silicon,tin, antimony or bismuth. X³ represents a halogen atom, such as achlorine atom, a bromine atom and an iodine atom. i represents an atomicvalency of M and is usually a real number of 1 to 5. k represents a realnumber of 0 <k ≦i.

Representative examples of the compounds represented by the generalformula (VI) are alkyllithium such as methyllithium, ethyllithium,propyllithium and butyllithium, alkylmagnesium such as diethylmagnesium,ethylbutylmagnesium, di-n-butylmagnesium, ethylchloromagnesium andethylbromomagnesium, dialkylzinc such as dimethylzinc, diethylzinc,dipropylzinc and dibutylzinc, alkylgallium such as trimethylgallium,triethylgallium, tripropylgallium and tributylgallium, alkylboron suchas triethylboron, tripropylboron and tributylboron, and alkyltin such astetraethyltin, tetrapropyltin, tributylchlorotin, tetraphenyltin andtriphenylchlorotin.

In a case where M is aluminum, representative examples of the compoundsof the general formula (VI) are trialkylaluminum such astrimethylaluminum, triethylaluminum, triisopropylaluminum,triisobutylaluminum and trioctylaluminum; dialkylaluminum monohalidesuch as diethylaluminum monochloride, diethylaluminum monobromide,diethylaluminum monoiodide, diisopropylaluminum monochloride,diisobutylaluminum monochloride and dioctylaluminum monochloride;alkylaluminum sesquihalide such as methylaluminum sequichloride,ethylaluminum sesquichloride, ethylaluminum sesquibromide andbutylaluminum sesquichloride; and alkylaluminum dichloride such asmethylaluminum dichloride, ethylaluminum dichloride, propylaluminumdichloride and butylaluminum dichloride. Mixtures of the above compoundsare also suitably used. In addition, alkyl group-containing aluminoxaneformed by the reaction of alkylaluminum and water can be used.

Of the above compounds, aluminum, tin and magnesium compounds areparticularly preferred.

There are not special limitations to the ratio of the transition metalcompound (a) to the organometallic compound (b) to be used in theprocess of the present invention. The ratio of the transition metalcompound (a) to the organometallic compound (b) is usually determined sothat the molar ratio of a metal atom contained in the organo-metalliccompound (b) to a chromium atom contained in the transition metalcompound (a) is 0.1/1 to 5,000/1 and preferably 1/1 to 1,000/1.

In accordance with the process of the present invention, ethylene andunsaturated carboxylic acid or esters thereof are copolymerized usingthe above catalyst in the presence of a Lewis acid to produce ethylenecopolymers.

Lewis acids which can be used include Lewis acid compounds capable offorming a complex with a lone electron pair of a polar group, such asGroup I, II, III, V or VIII metal halide. Aluminum, boron, zinc, tin,magnesium and antimony halides such as aluminum trichloride, aluminumtribromide, ethylaluminum dichloride, diethylaluminum dichloride, borontrichloride, zinc dichloride, tin tetrachloride, alkyltin halide,magnesium dichloride, antimony pentachloride and antimony trichlorideare preferred. Particularly preferred are aluminum trichloride, aluminumtribromide and ethylaluminum dichloride.

There are no special limitations to the unsaturated carboxylic acid orits ester which is to be copolymerized with ethylene. Usually the abovecompounds represented by the general formula (IV) are used. Morespecifically, compounds corresponding to the repeating unit (C) of theethylene copolymer to be produced are chosen. For example, an acrylicacid, a methyl acrylate, an ethyl acrylate, a n-propyl acrylate, aniso-propyl acrylate, a n-butyl acrylate, an iso-butyl acrylate, atert-butyl acrylate, a n-hexyl acrylate, a n-octyl acrylate, a2-ethylhexyl acrylate, a benzyl acrylate, a methacrylic acid, a methylmethacrylate, an ethyl methacrylate, a n-propyl methacrylate, aniso-propyl methacrylate, a n-butyl methacrylate, an iso-butylmethacrylate, a tert-butyl methacrylate, a 2-ethylhexyl methacrylate, aphenyl methacrylate, a methyl α-chloroacrylate, an ethylα-chloroacrylate, and a methyl α-phenylacrylate can be used singly or incombination with each other.

The ratio of the above unsaturated carboxylic acid or its ester toethylene is determined appropriately according to the physicalproperties of the desired ethylene copolymer.

The molar ratio of the above Lewis acid to the unsaturated carboxylicacid or its ester is 0.1/1 to 10/1 and preferably 0.2/1 to 1/1.

The process of the present invention is not critical in itscopolymerization manner; any of slurry polymerization, solutionpolymerization, gas polymerization and so forth can be employed, and anyof continuous polymerization and non-continuous polymerization can beemployed. In the practice of the process of the present invention bysolution polymerization, for example, aliphatic hydrocarbons, alicyclichydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons can beused as polymerization solvents. More specifically, pentane, hexane,peptane, octane, decane, dodecane, cyclohexane, benzene, toluene,xylene, ethylbenzene, chlorobenzene, ethylene dichloride, kerosene andthe like can be used.

In connection with polymerization conditions, the reaction pressure isatmospheric pressure to 100 kilograms per square centimeter by gauge(kg/cm² G) and preferably atmospheric pressure to 30 kg/cm² G, and thereaction temperature is -80° to 200° C. and preferably -50° to 60° C.The reaction time is not critical; usually it is chosen appropriatelyfrom the range of 1 minute to 10 hours. Controlling a molecular weightin the practice of the process of the present invention can be carriedout by known techniques such as by using hydrogen.

The ethylene copolymer of the present invention, which is produced bythe aforementioned process, possesses the aforementioned straight chainand random structure and, as compared with ethylene copolymers producedby the conventional high pressure radical polymerization method, has ahigh melting point (100° to 134° C.) and a high degree ofcrystallization (15 to 70%). Accordingly the ethylene copolymer of thepresent invention has a high mechanical strength and is also excellentin elasticity, and thus can be used for fabrication of industrialmaterials which are needed to have good printing properties, adhesionproperties and low temperature flexibility.

In accordance with the process of the present invention, the aboveethylene copolymer can be efficiently produced because the catalyticactivity is high, and furthermore the conversion of unsaturatedcarboxylic acid or its ester into the ethylene copolymer can beincreased.

EXAMPLE 1 (1) Preparation of Chromium-Containing Catalyst Component

A 300-milliliter (ml) flask the atmosphere of which had been replacedwith argon was charged with 1.1 grams (g) (4.45 millimoles (mmol)) ofchromium acetate monohydrate (Cr(CH₃ COO)₃ H₂ O), 40 ml of acetic acidand 40 ml of acetic anhydride, which were then reacted while stirringunder reflux for 20 hours. Then the acetic acid and acetic anhydridewere distilled away to obtain a green solid. This solid was dried at120° C. for 48 hours in a stream of argon. After the temperature waslowered, toluene was added to form 200 ml of a green catalyst slurry.(2) Production of Copolymer

800 ml of dehydrated toluene was introduced in a 1-liter stainless steelautoclave, and then 12.7 millimoles (mmol) of a toluene solution of amixture of equimolar amounts of ethyl acrylate and ball milled aluminumtrichloride was added. Then 8 mmol of diethylaluminum monochloride and0.2 mmol (calculated as chromium) of the chromium-containing catalystcomponent prepared in (1) above were introduced while maintaining thetemperature at 40° C. and stirring, and hydrogen gas was introduced andsaturated while stirring at a rate of 500 r.p.m. (rotations per minute)so that the hydrogen partial pressure was 1.0 kilograms per squarecentimeter by gauge (kg/cm² G). Then, ethylene was introduced so thatthe ethylene partial pressure was 2.0 kg/cm² G, thereby making the totalpressure 3 kg/cm² G.

Polymerization was conducted for 2 hours, and then the pressure wasremoved. The contents were introduced in methanol and precipitated. Theprecipitated solid was recovered by filtration and, after de-ashingtreatment using a hydrochloric acid-methanol mixture, was extracted withacetone for 5 hours to remove amorphous polymers. The extraction residuethus obtained was dried under reduced pressure at 80° C. for 2 hours toyield 1.82 g of a white polymer. In an infrared absorption spectrum ofthe white polymer (copolymer), an absorption peak at 1730 cm⁻¹ asassinged to a carbonyl group and an absorption peak at 1160 cm⁻¹ asassinged to an ether bond were observed. Based on the ratio of the aboveabsorption peaks to absorption peaks in the neighborhood of 720 cm⁻¹ and730 cm⁻¹ as assinged to a methylene chain, it was determined that theethyl acrylate content of the copolymer was 4.4 mol%. The melt index(MI) (2.16 kg) at 190° C. was 0.66 g per ten minutes (g/10 min). Themelting point of the copolymer, which was determined by heat treating at180° C. for 3 minutes in a nitrogen gas by the use of Model DSC IImanufactured by Perkin Elmer Co., Ltd., decreasing the temperature to50° C. for 5 minutes, and then measuring at a temperature-raising rateof 10° C. per minute, was 127° C. This value is lower by 8 ° C. than themelting point, 135° C., of polyethylene. This confirms that as a resultof random arrangement of the ethyl acrylate unit in the ethylene chainof the copolymer, the crystal form of the polyethylene portion isdisturbed.

The degree of crystallization of the above copolymer as calculated bythe symmetrical reflection method based on an X-ray diffraction(Rhotaflex 35 kilovolts (kv), 120 milliamperes (mA)) of a film which wasproduced by press molding at 190° C. and then annealing at 100° C. for10 minutes was 48.2%. The results are shown in Table 1.

EXAMPLE 2

The procedure of Example 1 (2) was repeated with the exception thatconditions were changed as shown in Table 1. The results are shown inTable 1.

EXAMPLE 3 (1) Preparation of Chromium-Containing Catalyst Component

In a 200-ml flask the atmosphere of which had been replaced with argonwas placed 2.1 9 (6 mmol) of chromium triacetylacetonate, and 200 ml oftoluene was added to dissolve therein the chromium triacetylacetonate.The solution thus prepared was used as a chromium-containing catalystcomponent in the subsequent reaction. (2) Production of Copolymer

The procedure of Example 2 was repeated with the exception that thechromium-containing catalyst component prepared in (1) above was used.The results are shown in Table 1.

EXAMPLE 4 (1) Preparation of Chromium-Containing Catalyst Component

In a 200-ml flask the atmosphere of which had been replaced with argonwere placed 10 stainless steel balls (diameter: 5-10 millimeters (mm))and then 3.6 g (4.0 mmol) of chromium stearate and 100 ml of toluene,which were then ball milled with stirring at room temperature for 10hours. After ball milling, toluene was added to make the total volume200 ml. As a result, a black purple gel-like product was obtained, andthis product was used as a chromium-containing catalyst component in thesubsequent reaction. (2) Production of Copolymer

The procedure of Example 2 was repeated with the exception that thechromium-containing catalyst component prepared in (1) above was used.The results are shown in Table 1.

EXAMPLE 5 (1) Preparation of Chromium-Containing Catalyst Component

0.556 g (1.61 mmol) of chromium tetra-tert-butoxide was dissolved in 50ml of toluene. The solution thus prepared was used as achromium-containing catalyst component in the subsequent reaction. (2)Production of Copolymer

The procedure of Example 2 was repeated with the exception that thechromium-containing catalyst component prepared in (1) above was used.The results are shown in Table 1.

EXAMPLE 6

(1) Preparation of Chromium-Containing Catalyst Component

In a 200-ml flask the atmosphere of which had been replaced with argon,1.22 g (6.7 mmol) of biscyclopentadienyl chromium was dissolved in 200ml of toluene. The solution thus prepared was used as achromium-containing catalyst component in the subsequent reaction.

(2) Production of Copolymer

The procedure of Example 2 was repeated with the exception that thechromium-containing catalyst component prepared in (1) above was used.The results are shown in Table 1.

EXAMPLE 7

The ethylene-ethyl acrylate copolymer produced in Example 1 (2) wascontacted with an aqueous sodium hydroxide solution (concentration: 60%by weight (wt%)) in ethanol at 80° C. for 3 hours, washed with dilutedhydrochloric acid, and then washed with water and dried to yield ahydrolysised product. An infrared absorption spectral analysis of theabove saponified product showed that the absorption peak in theneighborhood of 1730 cm⁻¹ as assinged to carboxylic acid ester (ethylacrylate) which had been observed before hydrolysis disappeared andinstead an absorption peak as assinged to the carbonyl group ofcarboxylic acid appeared in the neighborhood of 1700 cm⁻¹. Similarly, inthe 13_(C-NMR) spectrum, the peak based on the ester carbon disappeared.

Based on the above analytical results, it was confirmed that thehydrolysised product was an ethylene-acrylic acid copolymer. The meltingpoint of the copolymer as determined by the differential thermalanalysis was 128° C.

COMPARATIVE EXAMPLE 1

(1) Preparation of Vanadium-Containing Catalyst Component

A mixture of 80 ml of hexane and 0.66 ml (7 mmol) of vanadiumtrichloride was placed in a 300-ml flask, and then 3.9 ml of a hexanesolution of tri-n-butyl gallium (0.17 mmol/ml) was dropped over 30minutes. They were reacted at 20° C. for 3 hours, and a formed solidcomponent was washed five times with 100 ml of hexane and finally madeso that the total volume was 200 ml. The concentration of vanadium inthe above prepared catalyst slurry was 21 mmol/1. (2) Production ofCopolymer

300 ml of hexane and 2.67 g (20 mmol) of aluminum chloride were placedin an argon atmosphere in a 500-ml autoclave and then 2.17 ml (20 mmol)of ethyl acrylate was added. The resulting mixture was raised intemperature to 50° C. and stirred. Then, 2 mmol of triethyl aluminum wasadded, and furthermore 2.38 ml (0.05 mmol as vanadium) of the catalystslurry prepared in (1) above was added. Copolymerization was conductedat 50° C. for 3 hours while continuously introducing ethylene in such amanner that the total pressure became 2 kg/cm² G, After the completionof reaction, the pressure was decreased, and the product was washed witha methanol-hydrochloric acid mixture and extracted with acetone for 6hours. The extraction residue was dried to yield 5.35 g of a copolymer.

The properties of the above copolymer are shown in Table 1. The meltingpoint of the copolymer was 135° C., which is equal to that ofpolyethylene. The copolymer was a copolymer in which the ethyl acrylateunit was block polymerized to the ethylene chain. Analytical results ofthe ¹³ C-NMR spectra are shown in Table 2.

COMPARATIVE EXAMPLE 2

An ethylene-ethyl acrylate copolymer produced by the high pressureradical polymerization method (ethyl acrylate unit content: 2 mol%;produced by Nippon Unicar Co., Ltd.; trade name: NUC 6220) was measuredfor properties. The results are shown in Table 1, and a ¹³ C-NMRspectrum of the copolymer is shown in FIG. 3.

Analytical results of the ¹³ C-NMR spectra are shown in Table 2.

                                      TABLE 1                                     __________________________________________________________________________                         Aluminum-                                                Chromium-Containing  Containing                                               Catalyst             Catalyst  Reaction                                                                            Ethylene                                                                            Hydrogen                                                                            Amount of                    Component            Component Tempera-                                                                            Feed  Feed  Ethyl                                        Amount    Amount                                                                             ture  Pressure                                                                            Pressure                                                                            Acrylate                     Run No.                                                                             Type      (mmol)                                                                             Type (mmol)                                                                             (°C.)                                                                        (kg/cm.sup.2 G)                                                                     (kg/cm.sup.2 G)                                                                     (mmol)                       __________________________________________________________________________    Example 1                                                                           Cr(OAc).sub.3 /Ac.sub.2 O*.sup.1                                                        0.2  DEAC*.sup.6                                                                        8.0  40    2.0   1.0   12.7                         Example 2                                                                           Cr(OAc).sub.3 /Ac.sub.2 O*.sup.1                                                        0.2  DEAC*.sup.6                                                                        8.0  20    2.0   2.0   26.7                         Example 3                                                                           Cr(acac).sub.3 *.sup.2                                                                  0.2  DEAC*.sup.6                                                                        8.0  20    2.0   2.0   26.7                         Example 4                                                                           CrSt.sub.3 *.sup.3                                                                      0.2  DEAC*.sup.6                                                                        8.0  20    2.0   2.0   26.7                         Example 5                                                                           Cr(O.t-Bu)*.sup.4                                                                       0.2  DEAC*.sup.6                                                                        8.0  20    2.0   2.0   26.7                         Example 6                                                                           Cp.sub.2 Cr*.sup.5                                                                      0.2  DEAC*.sup.6                                                                        8.0  20    2.0   2.0   26.7                         __________________________________________________________________________                              Properties of Copolymer                                                       Ethyl                                                      Amount of          Acrylate         Weight                                                                              Degree of                           Alumium                                                                              Yield of                                                                            Catalytic                                                                           Unit Melting     Average                                                                             Crystalli-                          Trichloride                                                                          Copolymer                                                                           Activity                                                                            Content                                                                            Point MI    Molecular                                                                           zation                       Run No.                                                                              (mmol) (g)   (kg/g · Cr)                                                                (mol %)                                                                            (°C.)                                                                        (g/10 min)                                                                          Weight                                                                              (%)                          __________________________________________________________________________    Example 1                                                                            12.7   1.82  0.17  4.4  127   0.66  125000                                                                              48.2                         Example 2                                                                            26.7   4.27  0.41  3.2  128   2.15  79000 51.3                         Example 3                                                                            26.7   3.66  0.35  2.5  129   2.11  79000 53.5                         Example 4                                                                            26.7   2.51  0.24  3.1  128   2.03  80000 50.2                         Example 5                                                                            26.7   3.98  0.38  3.9  127   1.85  82000 49.1                         Example 6                                                                            26.7   3.25  0.31  2.8  129   1.54  85000 50.5                         Comparative               3.2  135   1.50  95000 52.0                         Example 1                                                                     Comparative               2.0   97   3.86  63000 22.6                         Example 2                                                                     __________________________________________________________________________     *.sup.1 Chromium acetate/acetate anhydride (prepared in Example 1 (1))        *.sup.2 Chromium triacetylacetonate (prepared in Example 3 (1))               *.sup.3 Chromium stearate (prepared in Example 4 (1))                         *.sup.4 Chromium tetratert-butoxide (prepared in Example 5 (1))               *.sup.5 Biscyclopentadienyl chromium (prepared in Example 6 (1))              *.sup.6 Diethylaluminum monochloride                                     

                                      TABLE 2                                     __________________________________________________________________________                                                Ethyl                                                                Alkyl Branch                                                                           (Ethyl                                   Principle Chain             (Long Chain)                                                                           Acrylate                                 Random CH.sub.2       homo CH.sub.2                                                                       CH.sub.2                                                                         CH.sub.2                                                                            Portion)                          Run No.                                                                              αε(ε.sup.+)                                                 γγ                                                                   γε(ε.sup.+)                                                 βδ(δ.sup.+)                                                      (CH.sub.2).sub.n                                                                  CH*                                                                              αα                                                                      α                                                                          β                                                                           CH.sub.3                                                                         CH.sub.2                                                                         CH.sub.3                       __________________________________________________________________________    Example 1                                                                            33.5                                                                              30 28.9                                                                              27.2                                                                              29.5                                                                              45.2                                                                             --    -- -- -- 59.3                                                                             14.0                           Comparative                                                                          --  -- --  --  29.5                                                                              43.6                                                                             34.6  -- -- -- 59.6                                                                             13.9                           Example 1                                                                     Comparative                                                                          32.4                                                                              30.1                                                                             29.5                                                                              29.2                                                                              27.4                                                                              45.4                                                                             --    34.3                                                                             27.0                                                                             14.2                                                                             59.2                                                                             13.6                           Example 2                                                                     __________________________________________________________________________

The structure of the ethylene-ethyl acrylate random copolymer is asfollows: ##STR12##

On the other hand, the structure of the ethyleneethyl acrylate blockcopolymer as produced in Comparative Example 1 is as follows: ##STR13##

Based on the above results, it can be understood that the ethylenecopolymer of the present invention possesses a straight chain structurewith almost no branch chain, which is clearly different from thebranched skeleton of the copolymer produced by the high pressure radicalpolymerization method. In connection with the principle chain, it isapparent that the copolymer possesses a random structure like thecopolymer of Comparative Example 2. EXAMPLE 8 (1) Preparation ofChromium-Containing Catalyst Component

A chromium-containing catalyst component slurry was prepared in the samemanner as in Example 1 (1). (2) Production of Copolymer

In a 1-liter stainless steel autoclave were introduced 800 ml ofdehydrated toluene, and then 19.2 mmol of a toluene solution of amixture of equimolar amounts of ethyl acrylate and aluminum trichloride.Then, 4 mmol of diethylaluminum chloride and 0.1 mmol of thechromium-containing catalyst component prepared in (1) above were addedwith stirring at 30° C. Then, the resulting mixture was saturated withhydrogen so that the hydrogen partial pressure was 2.0 kg/cm² G, andethylene was continuously introduced so as to maintain the totalpressure at 10 kg/cm² G. After polymerization was conducted for 3 hours,the pressure was removed, and a copolymer product was introduced inmethanol, filtered off and then was subjected to de-ashing treatmentusing a hydrochloric acid-methanol mixture. Then, extraction withacetone was conducted for 5 hours to thereby remove amorphous polymers.The extraction residue was dried under reduced pressure at 80° C. for 2hours to thereby obtain 20.6 g of a white copolymer.

In an infrared absorption spectrum of the above copolymer, an absorptionpeak as assigned to the carbonyl group of carboxylate was observed at1730 cm⁻¹ and an absorption peak as assigned to the ether bond, at 1160cm⁻¹. Based on these data, it was determined that the ethyl acrylatecontent of the copolymer was 2.5 mol%. In addition, in a nuclearmagnetic resonance spectral analysis using carbon isotope (¹³ C--NMR),the carbon signal of --CH₂ --of an ethyl branch was observed at 26.4 ppmand the carbon signal of --CH₃ terminal of an ethyl branch, at 10.7 ppm.Based on these data, it was confirmed that a degree of branching of thecopolymer was 8.9 per 1,000 of carbon atoms. The melting point of thecopolymer, which was determined by heat treating at 180° C. for 3minutes in nitrogen gas by the use of Model DSC II manufactured byPerkin Elmer Co., Ltd., decreasing the temperature to 50° C. in 5minutes, and then measuing at a temperature-raising rate of 10° C. perminute, was 128° C. The melt index of the copolymer was determined at190° C. under a load of 2.16 kg was 0.15 g/10 min.

The degree of crystallization of the above copolymer as calculated bythe symmetrical reflection method based on an X-ray diffraction(Rhotaflex 35 kv, 120 mA) of a film which was produced by press moldingthe copolymer at 190° C. and then annealing at lOO° C. for 10 minuteswas 50.4%. The results are

EXAMPLE 9

42.2 g of a copolymer was produced in the same manner as in Example 8(2) except that the amount of the toluene solution of a mixture ofequimolar amounts of ethyl acrylate and aluminum trichloride being usedwas 26.7 mmol, the polymerization temperature was 20° C., the hydrogenpartial pressure was 7 kg/cm² G, and the ethylene partial pressure was 3kg/cm² G.

The properties of the above copolymer are shown in Table 3.

EXAMPLE 10

20.4 g of a copolymer was produced in the same manner as in Example 8(2) except that the amount of the toluene solution of a mixture ofequimolar amounts of ethyl acrylate and aluminum trichloride being usedwas 26.7 mmol, the polymerization temperature was 20° C., the hydrogenpartial pressure was 8 kg/cm² G, and the ethylene partial pressure was 2kg/cm² G.

The properties of the above copolymer are shown in Table 3.

EXAMPLE 11

24.2 g of a copolymer was produced in the same manner as in Example 8(2) except that the amount of the toluene solution of a mixture ofequimolar amounts of ethyl acrylate and aluminum trichloride being usedwas 26.7 mmol.

The properties of the above copolymer are shown in Table 3.

EXAMPLE 12

8.04 g of a copolymer was produced in the same manner as in Example 8(2) except that the amount of the toluene solution of a mixture ofequimolar amounts of ethyl acrylate and aluminum trichloride being usedwas 64 mmol, the polymerization temperature was 20° C., the hydrogenpartial pressure was 2 kg/cm² G, and the ethylene partial pressure was 4kg/cm² G.

The properties of the above copolymer are shown in Table 3.

EXAMPLE 13

15.0 g of a copolymer was produced in the same manner as in Example 8(2) except that the amount of the toluene solution of a mixture ofequimolar amounts of ethyl acrylate and aluminum trichloride being usedwas 26.7 mmol, the hydrogen partial pressure was 4 kg/cm² G, and theethylene partial pressure was 6 kg/cm² G.

The properties of the above copolymer are shown in Table 3.

EXAMPLE 14

13.5 g of a copolymer was produced in the same manner as in Example 8(2) except that the amount of the toluene solution of a mixture ofequimolar amounts of ethyl acrylate and aluminum tricloride being usedwas 26.7 mmol, the hydrogen partial pressure was 5 kg/cm² G, and theethylene partial pressure was 5 kg/cm² G.

The properties of the above copolymer are shown in Table 3.

EXAMPLE 15

9.5 g of a copolymer was produced in the same manner as in Example 8 (2)except that the amount of the toluene solution of a mixture of equimolaramounts of ethyl acrylate and aluminum trichloride being used was 26.7mmol, the hydrogen partial pressure was 7 kg/cm² G, and the ethylenepartial pressure was 3 kg/cm² G.

The properties of the above copolymer are shown in Table 3.

EXAMPLE 16

8.9 g of a copolymer was produced in the same manner as in Example 8 (2)except that the amount of the toluene solution of a mixture of equimolaramounts of ethylacrylate and aluminum trichloride being used was 26.7mmol, the hydrogen partial pressure was 8 kg/cm² G and the ethylenepartial pressure was 2 kg/cm² G.

The properties of the above copolymer are shown in Table 3.

EXAMPLE 17

12.6 g of a copolymer was produced in the same manner as in Example 8(2) except that the amount of the toluene solution of a mixture ofequimolar amounts of 2-ethylhexyl acrylate and aluminum trichloridebeing used was 50 mmol, the hydrogen partial pressure was 4 kg/cm² G,and the ethylene partial pressure was 6 kg/cm² G. A proton nuclearmagnetic resonance (¹ H-NMR) spectral analysis of the copolymer showedthat the 2-ethylhexyl acrylate unit content of the copolymer was 7.4mol%. The melt index of the copolymer as determined at 190° C. under aload of 21.6 kg was 96.7 g/10 min. The melting point of the copolymer asdetermined by DSc was 119° C. The degree of crystallization of thecopolymer was 31%.

EXAMPLE 18

The copolymer produced in Example 8 was contacted with a 60 wt% aqueoussodium hydroxide solution at 80° C. for 3 hours in methanol and thenfully washed with diluted hydrochloric acid. Upon further application ofwashing with water and drying, a hydrolysised product was obtained. Inan infrared absorption spectrum of the above copolymer, an absorptionpeak at 1730 cm⁻¹ as assigned to the carbonyl group of carboxylic acidester which had been observed before the above hydrolysis disappearedand instead an absorption peak at 1700 cm⁻¹ as assigned to the carbonylgroup of carboxylic acid was observed. A ¹³ C-NMR spectral analysisshowed that the absorption peak at 14 ppm as assigned to the methylgroup of ester carbon which had been observed before the hydrolysisdisappeared. Based on the above data, it was understood that thesaponified polymer was an ethyleneacrylic acid copolymer. The meltingpoint of the ethylene-acrylic acid copolymer was 129° C.

The analytical results of the ¹³ C-NMR spectra are shown in Table 4.

                                      TABLE 3                                     __________________________________________________________________________           Ethyl Acrylate                                                                         Melt Index                                                                          Melting                                                                              Degree of                                        Run No.                                                                              Content (mol %)                                                                        (g/10 min)                                                                          Point (°C.)                                                                   Crystallization (%)                              __________________________________________________________________________    Example 8                                                                            2.5      0.15  128    50.4                                             Example 9                                                                            0.63     0.02  131    59.5                                             Example 10                                                                           1.0      0.02  131    56.5                                             Example 11                                                                           3.6      0.075 127    46.6                                             Example 12                                                                           5.8      0.002 126    45.1                                             Example 13                                                                           7.6      0.50  124    40.9                                             Example 14                                                                           9.3      0.85  123    39.5                                             Example 15                                                                           13.0     1.52  122    36.5                                             Example 16                                                                           15.0     2.58  121    33.9                                             __________________________________________________________________________

                                      TABLE 4                                     __________________________________________________________________________                                   Alkyl Branch                                                                           Ethyl Branch                          Principle Chain                (Long Chain)                                                                           (Principle Chain)                     Random CH.sub.2          homo CH.sub.2                                                                       CH.sub.2                                                                         CH.sub.2                                                                            Portion)                              Run No.                                                                             αε(ε.sup.+)                                                 γγ                                                                   γε(ε.sup.+)                                                 βδ(δ.sup.+)                                                      (CH.sub.2).sub.n                                                                  αα                                                                      α                                                                          β                                                                           CH.sub.3                                                                         CH.sub.2                                                                           CH.sub.3                         __________________________________________________________________________    Example 8                                                                           33.7                                                                              30.0                                                                             28.9                                                                              26.9                                                                              29.5                                                                              --    -- -- -- 26.4 10.7                             Example 17                                                                          33.7                                                                              30.0                                                                             28.9                                                                              26.9                                                                              29.5                                                                              --    -- -- -- 26.4 10.2                             __________________________________________________________________________

The structure of the ethylene-ethyl acrylate random copolymer is asfollows: ##STR14##

On the other hand, the structure of the ethyleneethyl acrylate blockcopolymer is, as described above, as follows: ##STR15##

Based on the above results, it can be seen that the copolymer producedin Example 8 has CH₂ in a random arrangement like the copolymer producedby the high pressure method as in Comparative Example 2. As can be seenfrom the results of Table 3, the melting points of the copolymersproduced in Examples 8 to 16 are lower than the melting point (135° C.)of the ethylene-ethyl acrylate block copolymer produced in ComparativeExample 1. This is due to the fact that in the copolymers of Examples 8to 16, the ethyl acrylate unit is bonded to the ethylene chain in arandom arrangement, thereby disturbing the crystal of the polyethyleneportion.

In a ¹³ C--NMR spectral analysis of the copolymer of Example 17, anabsorption peak as assigned to αε(ε⁺) is observed at 33.7 ppm, anabsorption peak as assigned to γγ, at 30.0 ppm, an absorption peak asassigned to γε(ε⁺), at 28.9 ppm, and an absorption peak as assigned toβδ(δ⁺), in the neighborhood of 26.9 ppm. This confirms that thecopolymer of Example 17 is a random copolymer.

EXAMPLE 19 (1) Preparation of Chromium-Containing Catalyst Component

A chromium-containing catalyst component slurry was prepared in the samemanner as in Example 4 (1). (2) Production of Copolymer

In a 500-ml reaction vessel the atmosphere of which had been replacedwith argon, 300 ml of toluene, 0.87 ml (8 mmol) of ethyl acrylate and 8mmol of ball milled aluminum chloride were placed. After purging severaltimes with argon at 20° C., 1 mmol of diethylaluminum chloride as theorganometallic compound component and 0.0025 mmol of the chromiumcatalyst component prepared in (1) above were added. Ethylene wasintroduced in the reaction vessel and polymerized for 3 hours whilemaintaining at 2 kg/cm² G. At the end of the time, the ethylene wasremoved and a product was precipitated with methanol. The solidcopolymer thus obtained was recovered by filtration and, after de-ashingtreatment using a hydrochloric acid/methanol mixture, amorphous polymerswere removed by extraction using acetone. The extraction residue wasdried under reduced pressure at 80° C. for 2 hours to obtain 1.13 g of awhite copolymer.

The catalyst activity was 8.7 kg/g. The copolymer thus obtained wassubjected to an infrared absorption spectral analysis. This analysisshowed an absorption peak at 1730 cm⁻¹ and an absorption peak at 1160cm⁻¹ as assigned to an ether bond. Based on these data, it wasdetermined that the ethyl acrylate content of the copolymer was 12.0 wt%and the conversion of ethyl acrylate to the copolymer was 17.0%(68.0%/0.01 mmol chromium). The melting point of the copolymer was 129°C. This is lower than the melting point (134° C.) of polyethyleneproduced using the same catalyst as above. A nuclear magnetic resonancespectral analysis showed that there was no peak assigned to an ethylbranch. Based on these data, it is believed that ethyl acrylate wasintroduced in the ethylene polymer chain in such a configuration as todisturb the crystal.

EXAMPLE 20

The procedure of (2) in Example 19 was repeated with the exception thatthe amount of the chromium catalyst component used was 0.005 mmol. Theresults are shown in Table 5.

EXAMPLE 21

The procedure of (2) in Example 19 was repeated with the exception thatthe amount of the chromium catalyst component used was 0.05 mmol. Theresults are shown in Table 5.

COMPARATIVE EXAMPLE 3

A vanadium-containing catalyst component was prepared in the same manneras in (1) of Example 19 except that 4.0 mmol of vanadium stearate wasused in place of chromium stearate. Subsequently, ethylene and ethylacrylate were copolymerized in the same manner as in (2) of Example 19except that 0.02 mmol of the above vanadium-containing catalystcomponent was used in place of the chromium catalyst component.

The yield of the copolymer was 5.6 g, catalyst activity was 5.5 kg/gvanadium, and the ethyl acrylate content of the copolymer was 0.1 wt%.The conversion of ethyl acrylate was 0.7% and the melting point of thecopolymer was 135° C.

COMPARATIVE EXAMPLE 4

A zirconium-containing catalyst component was prepared in the samemanner as in (1) of Example 19 except that 4.0 mmol of zirconiumstearate was used in place of chromium stearate. Subsequently, ethyleneand ethyl acrylate were copolymerized in the same manner as in (2) ofExample 19 except that 0.04 mmol of the above zirconium-containingcatalyst component was used in place of the chromium catalyst component.

The yield of the copolymer was 0.08 g, and catalyst activity was 0.022kg/g zirconium. The ethylacrylate content of the copolymer was 4.3 wt%,the conversion of ethyl acrylate was 4.3%, and the melting point of thecopolymer was 134° C.

EXAMPLE 22 (1) Preparation of Chromium Catalyst Component

A chromium-containing catalyst component slurry was prepared in the samemanner as in Example 1 (1). (2) Production of Copolymer

The procedure of (2) in Example 19 was repeated with the exception that0.00235 mmol of the catalyst slurry prepared in (1) above was used asthe chromium catalyst component. The results are shown in Table 5.

EXAMPLE 23

The procedure of (2) in Example 19 was repeated with the exception that0.0047 mmol of the catalyst slurry prepared in (1) of Example 22 wasused as the chromium catalyst component. The results are shown in Table5.

EXAMPLE 24

The procedure of (2) in Example 19 was repeated with the exception that0.047 mmol of the catalyst slurry prepared in (1) of Example 22 was usedas the chromium catalyst component. The results are shown in Table 5.

EXAMPLE 25

The procedure of Example 22 was repeated with the exceptions that theamount of diethylaluminum chloride as the organometallic compoundcomponent used was 0.5 mmol and the ethylene partial pressure wasmaintained at 3 kg/cm² G. The results are shown in Table 5.

EXAMPLE 26

The procedure of Example 23 was repeated with the exception 1 mmol oftriethylaluminum was used in place of the diethylaluminum chloride asthe organometallic compound component. The results are shown in Table 5.

EXAMPLE 27

The procedure of Example 24 was repeated with the exception that 3.0mmol of tetraethyltin was used in place of diethylaluminum chloride asthe organometallic compound component. The results are shown in Table 5.

EXAMPLE 28

The procedure of Example 23 was repeated with the exception that 3.0mmol of butylethylmagnesium was used in place of diethylaluminumchloride as the organometallic compound component. The results are shownin Table 5.

EXAMPLE 29

The procedure of Example 23 was repeated with the exception that 8 mmolof methyl methacrylate was used in place of ethyl acrylate as theunsaturated carboxylic acid ester. The results are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________                                   Conversion of                                         Yield of                                                                            Catalytic                                                                           Unsaturated Carboxylic                                                                    Unsaturated                                                                            Melting Point                                Copolymer                                                                           Activity                                                                            Acid Ester  Carboxylic Acid                                                                        of Copolymer                          Run No.                                                                              (g)   (kg/g Cr)                                                                           Content (wt %)                                                                            Ester (%)*.sup.1                                                                       (°C.)                          __________________________________________________________________________    Example 19                                                                           1.13  8.7   12.0        17.0 (68.0)                                                                            129                                   Example 20                                                                           1.19  4.6   7.8         11.6 (23.2)                                                                            130                                   Example 21                                                                           3.32  1.3   5.1         21.2 (4.2)                                                                             131                                   Example 22                                                                           1.19  9.7   11.4        17.0 (72.3)                                                                            129                                   Example 23                                                                           2.29  9.4   6.7         19.2 (40.8)                                                                            130                                   Example 24                                                                           2.95  1.2   5.8         21.4 (4.6)                                                                             130                                   Example 25                                                                           3.31  27.1  5.0         20.7 (88.1)                                                                            130                                   Example 26                                                                           3.14  12.8  2.9         11.4 (24.2)                                                                            131                                   Example 27                                                                           4.53  1.9   5.1         28.9 (6.1)                                                                             130                                   Example 28                                                                           1.15  4.7   6.4          9.2 (19.6)                                                                            130                                   Example 29                                                                           0.31  1.3   3.4         1.3 (2.8)                                                                              130                                   Comparative                                                                          5.6   5.5   0.1          0.7 (0.35)                                                                            135                                   Example 3                                                                     Comparative                                                                          0.08  0.022 4.3         0.4 (0.1)                                                                              134                                   Example 4                                                                     __________________________________________________________________________     *.sup.1 Conversion (%) per 0.01 mmol of the chromium catalyst component  

EXAMPLE 30 (1) Preparation of Catalyst Component

A 200-milliliter (ml) flask the atmosphere of which had been replacedwith argon gas was charged with 2.1 grams (g) (6 millimoles (mmol)) ofchromium triacetylacetonate, and then 200 ml of toluene was added andthe chromium triacetylacetonate was dissolved therein. The solution thusprepared was used as the chromium catalyst component in the subsequentreaction. (2) Production of Ethylene Copolymer

In a 500-ml pressure glass vessel the atmosphere of which had beenreplaced with argon gas, 300 ml of toluene and 0.87 ml (8 mmol) of ethylacrylate were placed and 8 mmol of ball-milled aluminum trichloride wasplaced in a stream of argon, and then 0.5 mmol of diethylaluminummonochloride and 0.0025 mmol of the chromium catalyst component preparedin (1) above were added. Then, ethylene was introduced in the pressureglass vessel and polymerized at 20° C. for 3 hours while maintaining thepressure at 2 kg/cm² G. At the end of the time, ethylene was purged andthe reaction mixture was poured into methanol to precipitate thereaction product. The solid copolymer thus obtained was recovered byfiltration and was subjected to de-ashing treatment using a hydrochloricacid/ methanol mixture, and then was extracted with acetone for 5 hoursto remove amorphous polymers. The residue after extraction was driedunder reduced pressure at 80° C. for 2 hours to obtain 1.32 g of a whitecopolymer. Catalytic activity (polymerization activity) was 10.1 kg/gchromium.

The copolymer thus obtained was subjected to an infrared absorptionspectral analysis. This analysis showed an absorption peak at 1730 cm⁻¹as assigned to a carbonyl group and an absorption peak at 1160 cm⁻¹ asassigned to an ether bond. Based on these peaks, it was confirmed thatthe ethyl acrylate content of the copolymer was 9.0% by weight (wt%) andthe conversion of ethyl acrylate into the copolymer 59.6%/0.01 mmolchromium. The melting point of the copolymer was 130° C. This is lowerthan the melting point (135° C.) of polyethylene produced using the samecatalyst as above. In a nuclear magnetic resonance spectral analysis, apeak as assigned to an ethyl branch was not observed. Based on thesedata, it is believed that ethyl acrylate was introduced in the ethylenepolymer chain in such a configuration as to disturb the crystal. Theabove results are shown in Table 6.

EXAMPLE 31

The procedure of (2) in Example 30 was repeated with the exception that0.5 mmol of triethylaluminum was used in place of diethylaluminummonochloride, thereby producing 1.10 g of a copolymer. This copolymerwas measured for polymerization activity and so forth in the same manneras in Example 30. The results are shown in Table 6.

EXAMPLE 32

The procedure of (2) in Example 30 was repeated with the exception that0.5 mmol of triisobutylaluminum was used in place of diethylaluminummonochloride, thereby producing 1.56 g of a copolymer. This copolymerwas measured for polymerization activity and so forth in the same manneras in Example 30. The results are shown in Table 6.

EXAMPLE 33

The procedure of (2) in Example 30 was repeated with the exceptions thatthe amount of the chromium catalyst component used was 0.005 mmol, theamount of the diethylaluminum monochloride used was 1.0 mmol, the amountof the ethyl acrylate used was 20 mmol, and the amount of the aluminumtrichloride used was 20 mmol, thereby producing 0.85 g of a copolymer.This copolymer was measured for polymerization activity and so forth inthe same manner as in Example 30. The results are shown in Table 6.

EXAMPLE 34

The procedure of (2) in Example 30 was repeated with the exceptions thatthe amount of the chromium catalyst component used was 0.005 mmol and 8mmol of methyl methacrylate was used in place of the ethyl acrylate,thereby producing 1.21 g of a copolymer. This copolymer was measured forpolymerization activity and so forth in the same manner as in Example30. The results are shown in Table 6.

EXAMPLE 35

The procedure of (2) in Example 30 was repeated with the exceptions thatthe amount of the chromium catalyst component used was 0.005 mmol and1.0 mmol of tetraethyltin was used in place of the diethylaluminummonochloride, thereby producing 0.92 g of a copolymer. This copolymerwas measured for polymerization activity and so forth in the same manneras in Example 30. The results are shown in Table 6.

EXAMPLE 36

The procedure of (2) in Example 30 was repeated with the exceptions thatthe amount of the chromium catalyst component used was 0.005 mmol and 1mmol of butylethylmagnesium was used in place of the diethylaluminummonochloride, thereby producing 0.63 g of a copolymer. This copolymerwas measured for polymerization activity and so forth in the same manneras in Example 30. The results are shown in Table 6.

EXAMPLE 37 (1) Preparation of Catalyst Component

A chromium-containing catalyst component slurry was prepared in the samemanner as in Example 5 (1). (2) Production of Copolymer

The procedure of (2) in Example 30 was repeated with the exceptions that0.005 mmol of the solution prepared in (1) above was used as thechromium catalyst component and the amount of the diethylaluminummonochloride used was 1 mmol, thereby producing 3.44 g of a copolymer.This copolymer was measured for polymerization activity and so forth inthe same manner as in Example 30. The results are shown in Table 6.

EXAMPLE 38 (1) Preparation of Catalyst Component

In a 200-ml flask the atmosphere of which had been replaced with argon,0.95 g (6 mmol) of chromium trichloride was placed. Subsequently, 10stainless steel balls (diameter: 5-8 mm) were placed and then 150 ml oftoluene was added. The resulting mixture was ball milled with stirringat room temperature for 24 hours. The solution thus prepared was used asthe chromium catalyst component in the subsequent reaction. (2)Production of Copolymer

The procedure of (2) in Example 30 was repeated with the exceptions that0.005 mmol of the solution prepared in (1) above was used as thechromium catalyst component and the amount of the diethylaluminummonochloride used was 1 mmol, thereby producing 0.64 g of a copolymer.This copolymer was measured for polymerization activity and so forth inthe same manner as in Example 30. The results are shown in Table 6.

EXAMPLE 39 (1) Preparation of Catalyst Component

A chromium-containing catalyst component solution was prepared in thesame manner as in Example 6 (1). (2) Production of Copolymer

The procedure of (2) in Example 30 was repeated with the exceptions that0.005 mmol of the solution prepared in (1) above was used as thechromium catalyst component and the amount of the diethylaluminummonochloride used was 1 mmol, thereby producing 1.9 g of a copolymer.This copolymer was measured for polymerization activity and so forth inthe same manner as in Example 30. The results are shown in Table 6.

EXAMPLE 40 (1) Preparation of Catalyst Component

In a 200-ml flask the atmosphere of which had been replaced with argon,1.51 g (7.33 mmol) of diphenylchromium was dissolved in 200 ml oftoluene. The solution thus prepared was used as the chromium catalystcomponent in the subsequent reaction. (2) Production of Copolymer

The procedure of (2) in Example 30 was repeated with the exceptions that0.005 mmol of the solution prepared in (1) above was used as thechromium catalyst component and the amount of the diethylaluminummonochloride used was 1 mmol, thereby producing 1.48 g of a copolymer.This copolymer was measured for polymerization activity and so forth inthe same manner as in Example 30. The results are shown in Table 6.

COMPARATIVE EXAMPLE 5

The procedure of (2) in Example 30 was repeated with the exception that0.0025 mmol of vanadium bisacetylacetonate was used in place of thechromium catalyst component, thereby producing 0.46 g of a copolymer.This copolymer was measured for polymerization activity and so forth inthe same manner as in Example 30. The results are shown in Table 6.

COMPARATIVE EXAMPLE 6

The procedure of (2) in Example 30 was repeated with the exception that0.0025 mmol of vanadium trichloride was used in place of the chromiumcatalyst component, thereby producing 0.06 g of a copolymer. Thiscopolymer was measured for polymerization activity and so forth in thesame manner as in Example 30. The results are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                                                     Conversion                                                          Unsatu-   of Unsatu-                                                          rated     rated                                                     Polymer-  Car-      Carbox-                                                   ization   boxylic   ylic Acid                                                                             Melting                                           Activity  Acid      Ester (%/                                                                             Point of                                          (kg/g     Content   0.01 mmol                                                                             Copolymer                                Run No.  chromium) (wt %)    chromium)                                                                             (°C.)                             ______________________________________                                        Example 30                                                                             10.1      9.0       59.6    130                                      Example 31                                                                             8.5       10.3      56.7    130                                      Example 32                                                                             12.0      6.2       48.4    131                                      Example 33                                                                             3.3       14.4      12.2    129                                      Example 34                                                                             9.3       6.8       41.1    131                                      Example 35                                                                             3.5       7.3       16.8    130                                      Example 36                                                                             2.4       8.4       13.1    130                                      Example 37                                                                             13.2      9.0       77.4    130                                      Example 38                                                                             4.9       5.6       17.9    131                                      Example 39                                                                             7.3       4.5       21.4    131                                      Example 40                                                                             5.7       6.2       22.9    130                                      Comparative                                                                            3.6       0.3       0.7     135                                      Example 5                                                                     Comparative                                                                            0.47      0.1       0.3     135                                      Example 6                                                                     ______________________________________                                    

What is claimed is:
 1. An ethylene copolymer consisting essentially ofarepeating unit (A) represented by the formula:

    --CH.sub.2 --CH.sub.2 --;

a repeating unit (B) represented by the formula: ##STR16## (wherein R¹represents an alkyl group having 1 to 20 carbon atoms); and a repeatingunit (C) represented by the formula: ##STR17## (wherein R² represents ahydrogen atom, a halogen atom, an alkyl group having 1 to 20 carbonatoms, an alkenyl group having 3 to 20 carbon atoms, a cycloalky grouphaving 3 to 20 carbon atoms, an aryl group having 6 to 20 carbon atomsor an aralkyl group having 7 to 20 carbon atoms, and R³ represents ahydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenylgroup having 3 to 20 carbon atoms, a cycloalkyl group having 3 to 20carbon atoms, an aryl group having 6 to 20 carbon atoms or an aralkylgroup having 7 to 20 carbon atoms), said repeating units (A), (B) and(C) being orientated in a random and straight chain arrangement, saidrepeating unit (B) content being 0 to 45 mol%, said repeating unit (C)content being 0.001 to 45 mol%, and said copolymer having a weightaverage molecular weight of at least 5,000.
 2. The ethylene copolymer asclaimed in claim 1, consisting of the repeating units (A) and (C) only.3. The ethylene copolymer of claim 1 wherein said repeating unit (C)content is at least 0.1%.
 4. The ethylene copolymer of claim 1 whereinsaid repeating unit (C) content is at least 1%.
 5. The ethylenecopolymer of claim 1 wherein said repeating unit (B) content is 0 to 30mole % and said repeating unit (C) content is 0.1 to 30 mole %.
 6. Theethylene copolymer of claim 1 wherein said repeating unit (C) content is0.1 to 30 mole %.
 7. The ethylene copolymer of claim 1 wherein saidrepeating unit (C) content is 1 to 15 mole %.
 8. The ethylene copolymerof claim 7 wherein said repeating unit (B) content is 0 to 15 mole %. 9.The ethylene copolymer of claim 8 wherein said weight average molecularweight is 10,000 to 3,000,000.
 10. The ethylene copolymer of claim 1wherein said weight average molecular weight is 10,000 to 3,000,000. 11.The ethylene copolymer of claim 2 wherein said repeating unit (C)content is at least 0.1%.
 12. The ethylene copolymer of claim 2 whereinsaid repeating unit (C) content is at least 1%.
 13. The ethylenecopolymer of claim 2 wherein said repeating unit (C) content is 0.1 to30 mole %.
 14. The ethylene copolymer of claim 2 wherein said repeatingunit (C) content is at 1 to 15 mole %.
 15. The ethylene copolymer ofclaim 2 wherein said weight average molecular weight is 10,000 to3,000,000.